Our Planet’s Eye In the Sky Finally Closes

taly’s Etna Volcano is seen erupting in image taken with the Advanced Land Imager (ALI) on NASA’s Earth Observing-1

Earth Observing-1 wasn’t supposed to survive as long as it did. Operating on a shoestring budget, the spartan satellite outlasted its warranty 15-fold, and changed the way we do space-based imaging of our planet.

The satellite trained its observant lens on the ashes of the 9/11 terrorist attacks. It captured the flood that followed in Hurricane Katrina’s wake. It took stock of the devastating tsunami that hit Japan in 2011. It was the first to map active lava flows from space, and the first to track re-growth in the deforested Amazon.

But all things must pass. EO-1 shut down last Thursday, in orbit, some 440 miles above Earth. It was 17.

“I was the first signatory on the decommissioning page, which was a little sad,” says Betsy Middleton, project scientist for EO-1 at NASA’s Goddard Space Flight Center. “We’re really bummed, but I managed to get two more years by all but throwing myself down in front of the last senior review and kicking and flailing.”

A fleet of watchful human-built satellites surrounds our planet, studying its landscapes, oceans and atmosphere on behalf of researchers, corporations, and governments. Some of the best-known American ones are the Landsat probes, which have been taking pictures of Earth since July 1972. Others include Terra and Aqua, which view the entire Earth’s surface every one to two days, and the Orbiting Carbon Observatory-2, which monitors global carbon dioxide levels. EO-1 was built as a test satellite to show off technologies suited to these pricier, more robust orbiters.

It carried a new type of camera now in use aboard Landsat-8, among others. It tested new strategies for calibrating satellite data, for flying in formation with other satellites, and for working autonomously.

“EO-1 has just been a learning experience, all the way around,” Middleton says.

An EO-1 image of the Great Blue Hole in Belize (NASA)

One of EO-1’s key goals was studying the ability of hyperspectral imaging to study Earth’s processes. That means looking at swathes of the Earth in different wavelengths of light, bundled together into spectral bands. Multi-spectral cameras look at Earth in lots of different wavelengths, but they don’t overlap. But on EO-1, they did, explains Middleton.

“We can pick any darn band we want, and we can average them. That’s a big advantage,” she says.

The result is the planet in technicolor, giving researchers a full spectrum of data on what plants are doing, how ecosystems are faring, where fires are spreading, whether methane or other gases are leaking, whether volcanoes are erupting, and more.

An EO-1 image of Sendai, Japan after the 2011 tsunami (NASA)

EO-1 was so good at this, scientists are now designing a satellite to follow in its footsteps, called the Hyperspectral Infrared Imager, which will study the world’s ecosystems.

Along with testing new technologies, EO-1 occasionally filled in for its more sophisticated satellite siblings. It was special because it could fly over any particular area every two to five days, and could be pointed anywhere, which was useful for disaster management and science. Landsat probes can only view the same area every 16 days. This came in handy when, for instance, EO-1 captured some of the first images of Sendai, Japan, after the 2011 tsunami.

The satellite also captured these shots of Iceland’s Eyjafjallajökull volcano during its 2010 eruption.

The 2010 eruption of Iceland’s Eyjafjallajökull volcano (NASA)

While Landsat collects continuous images over land, it does not observe the ocean, as its name implies. This means it can miss remote islands. EO-1 was able to help with that, too. During Global Land Survey projects in 2005 and 2010 — like a landscape census — EO-1 was tasked with taking photos of small islands strewn about the Pacific Ocean that had never been viewed at high resolution.

A satellite’s view of Earth is more complicated than snapping a photo. Satellites sense things like minerals and the chemical process of photosynthesis, and computer programs stitch this raw data into a form that scientists can interpret. Middleton, a botanist who has also worked with Landsat and other Earth observers, studies how satellites look at vegetation and the ways their signals can be confused by reflected sunlight and warmth, or by different viewing angles. She says EO-1 was useful in part because its cameras observed Earth in small chunks. One of its instruments captured data in strips just 4.3 miles wide, which are easier to contrast with aerial views; other satellites view Earth in strips that are tens of miles across.

“That’s one reason why researchers have loved [EO-1]. It’s not all that different from an aircraft strip,” she says. “For people who would like a satellite view of an area, that gives them the spatial context of where their study area fits in the region, and it’s in high enough resolution that you can define communities and ecosystems.”

EO-1 was able to study changes to these ecosystems, especially the effects of climate change. This EO-1 image shows plant communities in Barrow, Alaska, and how their productivity changes as permafrost thaws.

(NASA)

Initially, EO-1 images cost $1,100 each, but with improved processing, the price tag had dropped to $750 by 2009. In 2010, the EO-1 team worked with the U.S. Geological Survey to make the satellite’s images freely available. In 2015 alone, researchers and the public downloaded 250,000 images, and used them to study floods and mudslides. and to distinguish different types of plants growing in forests and plains, and to glimpse vegetation changes at international borders.

Despite its popularity, EO-1 had a small budget, Middleton says. “We’ve only had a small team at Goddard, me and five or six other people, and then people in the engineering group. We’ve had to be creative and figure out how to make things automated.”

Middleton and her team automated some of the image processing, but they also automated the satellite itself. EO-1 was the first Earth observer to make its own decisions based on the data it collected. If a scientist directed EO-1 to photograph a volcanic eruption, for instance, the satellite could use its software to decide whether to take follow-up photos when it flew over the same location a few days later. The EO-1 team also developed a network connecting their satellite to other Earth observers, so they could trigger each other to take pictures.

EO-1 is survived by the DSCOVR satellite, the Orbiting Carbon Observatory-2, Terra and Aqua, and several Landsat probes. But some of its Earth-observing kin might face a similar fate, albeit for very different reasons.

The federal budget proposed by the Trump Administration zeroes out funding for a new satellite called the Orbiting Carbon Observatory-3. The budget also would shut down the Earth-observing instruments aboard the Deep Space Climate Observatory, or DSCOVR, whose main goal is studying the solar wind. DSCOVR orbits in a gravitational sweet spot between the Earth and the sun, a vantage point that allows for an hour’s warning of a solar storm, as well as beautiful views of our cloud-swirled home world and our moon.

The original plan was to shut down EO-1 after a year to 18 months, by which point NASA engineers figured something would have gone wrong. In the early days of the mission, an instrument that corrected images for atmospheric distortion failed, so mission managers just stopped using it. Otherwise, EO-1 kept humming along, with a shoestring budget and a small team of engineers and scientists to work on it and process its images.

By February 2011, EO-1 was running low on fuel, and began to drift. Since then, it has started to slowly lose elevation, as the thinnest wisps of Earth’s upper atmosphere gradually slow it down in a process called orbital decay. Normally, a satellite is decommissioned once it’s out of fuel to control its orbit, but Middleton and her team were able to convince NASA to keep it going.

Even in death, EO-1 has continued producing riches to improve human understanding: Engineers studied its orbital decay in its last days, as they have with no other satellite. Last year, some people at NASA debated using the satellite as a lunar observer until it burns up in the atmosphere, but this was ruled out.

EO-1 was powered off March 30, but it will remain in Earth’s orbit until 2056, when it will fall so low that it will begin to burn up in the atmosphere. In lieu of flowers, Middleton is planning a satellite wake for June 7 at Goddard.

“We’ll be inviting people who were involved way back, 20 years ago in planning the mission. We’ll have few talks, but it will be a party,” she says. She wants to set up a TV screen with a slideshow of EO-1 images, but she couldn’t say which one was her favorite.

“It depends on what you like, nature or urban. There’s one of downtown Baltimore, the harbor, we used that one on the cover of a publication. There are islands that are just gorgeous,” she says. “You’ll just have to look and see how beautiful they are.”